The invention relates to a tire pressure controlling device for a tire of a vehicle wheel filled with compressed air, including a control valve unit for filling the tire with compressed air and/or venting same therefrom. The compressed air is fed by a compressor device for producing the tire filling pressure. Furthermore, the invention also relates to a method for filling a tire with compressed air, and also to a commercial vehicle trailer which is provided with the tire pressure controlling device.
The field of use of the invention extends primarily to commercial vehicle technology. A compressed air system is already present for a generally pneumatic braking system of a commercial vehicle, the compressed air system generally being fed via its own onboard compressor which is customarily driven via the internal combustion engine of the commercial vehicle. The compressed air produced by this means is generally not solely available only to the pneumatic braking system; for example, a pneumatic suspension device for the vehicle wheels and a tire pressure controlling device, which is of interest within the scope of the present invention, can also be fed in addition thereto.
According to current regulations, the system pressure level of the vehicle compressed air system is limited to a maximum of 8.5 bar. A load-dependent filling of the tires by the tire pressure controlling device takes place depending on the loading of the vehicle. By this means, a lower tire pressure is set in the event of small loading of the vehicle than in the event of higher loading of the vehicle. Since, for this load-dependent filling of the tires with compressed air, pressure levels above the maximum system pressure level of 8.5 bar are also required, namely of up to 9.5 bar, depending on the type of tire, the system pressure level does not suffice for operating the tire pressure controlling device.
WO 01/70521 A1 reveals a tire pressure controlling device with an additional booster device. The booster device is designed as a special pressure intensifier pump with an inlet and an outlet for intensifying the air pressure of the supply of air to the tire. The inlet is connected here to the system pressure supply of the vehicle and the outlet is connected to the tire. The pressure intensifier pump is designed as an alternating piston pressure pump and increases the air pressure by the desired amount above the system pressure. Due to the design, this pressure intensifier pump produces a high loss of compressed air of approximately half of the system compressed air supplied on the input side. This leads to a high consumption of energy.
U.S. Pat. No. 8,528,611 B2 discloses another solution for a tire pressure controlling device with an additional compressor device for producing a high pressure level, which exceeds the system pressure level, for filling the tires. However, in this case, the compressor device is not fed by the system pressure but rather extracts the air to be compressed from the atmosphere. In principle, use is made here only of a separate additional compressor which, because of the drive additionally also required, causes an increased outlay on apparatus technology in comparison to a booster device described above as prior art.
It is therefore the object of the present invention to further improve a tire pressure controlling device of the type in question to the effect that, with a minimal outlay on apparatus technology, a needs-based energy-saving supply of compressed air for filling tires to a high pressure level exceeding the system pressure level is made possible.
The object is achieved by a tire pressure controlling device, a method of operating same, and a commercial vehicle having the tire pressure controlling device, for a vehicle wheel tire charged with compressed air, comprising a control valve unit for controlled filling of the tire with compressed air and/or venting same therefrom, the compressed air being fed by a compressor for producing the tire filling pressure. The compressor for compressing drawn in air from the atmosphere is driven by mechanical rotational movement of the vehicle wheel via a transmission unit arranged therebetween that transmits the rotational driving movement from the vehicle wheel to the drive shaft of the compressor.
The invention includes the technical teaching that the compressor for producing the tire filling pressure is driven by the mechanical rotational movement of the vehicle wheel by a transmission unit arranged in-between that transmits the rotating driving movement of the vehicle wheel to the drive shaft of the compressor.
The advantage of the solution according to the invention resides in particular in the fact that the rotational movement of the vehicle wheel that is present in any case during movement of the vehicle is used, by said rotational movement being branched off via the transmission unit, in order to operate the compressor. By this means, the tire pressure controlling device is independent of the system pressure ps and can also be provided with a higher pressure level, depending on the power configuration of the compressor, and therefore the maximally achievable tire filling pressure pr can be greater than the system pressure ps which can then primarily be used for operating a pneumatic braking system and/or suspension system.
The transmission unit for transmitting the mechanical rotational movement of the vehicle wheel to the drive shaft of the compressor can be designed, for example, as a toothed transmission. This embodiment is appropriate if the transmission unit can be placed in close proximity to the vehicle wheel. If this is not the case and insofar as a greater power transmission distance has to be bridged, it is proposed to design the transmission unit as a chain or belt transmission. Should accommodating the moving traction wheels at the installation location of the tire pressure controlling device be inconvenient, an alternative thereto is to design the transmission unit as a hydraulic pump and hydraulic motor arrangement. In this case, the fluidic power transmission takes place via pressure medium lines which can be accommodated in a fixedly laid manner in the region of the vehicle. The hydraulic pump part of said transmission unit should then be placed in close proximity to the vehicle wheel and the hydraulic motor part should preferably be mounted directly on the drive shaft of the transmission unit.
Furthermore, it is also contemplated to design the transmission unit as an electric generator and motor arrangement. In this case, for the transmission of power, an electric line should be laid in the region of the vehicle. The generator part of said transmission unit should be placed in the region of the vehicle wheel, whereas the motor part can be attached to the drive shaft of the transmission unit. In all of the cases, the transmission unit ensures that a tire pressure controlling device can be realized which can be operated independently of the system pressure network or power supply network of the vehicle and can be driven in a simple manner by the movement of the vehicle wheel in a need-controlled manner.
According to a measure improving the invention, an air dryer unit is connected on the air outlet side of the compressor. The air dryer unit provides for drying of the air drawn-in from the atmosphere by the compressor device before the connected tire is filled therewith. The compressed air which is dried to this extent minimizes the corrosion within the tire pressure controlling device in comparison to undried compressed air. Air is drawn-in from the atmosphere preferably via an air filter arranged on the air inlet side of the compressor.
In order only to put the tire pressure controlling device into operation when needed, it is proposed to arrange a coupling device between the transmission unit and the vehicle wheel driving the latter. The coupling device is preferably actuated by the compressed air need of the tire. This means that the coupling between the vehicle wheel and the transmission unit is connected whenever the tire filling pressure pr drops below a defined minimum limit. By contrast, the coupling device disconnects whenever the tire filling pressure pr has reached a defined maximum value of, for example, 9.5 bar. This technical solution provides a simple and robust needs-based activation of the tire filling. As an alternative thereto, it is also contemplated to activate the coupling device via an electric control signal in order to put said coupling device into operation when needed.
In addition, the operating state of the transmission unit can be monitored via a suitable sensor arrangement, for example a revolution counter, in order to determine whether mechanical driving energy is or is not present as a consequence of a movement of the vehicle. This information can be made use of by a master controller for the electric activation of the tire pressure controlling device. This is because, in the solution according to the invention, a movement of the vehicle is a prerequisite for the tire pressure controlling device to be able to be put into operation—preferably via closing of the coupling device.
The solution according to the invention is preferably used in a commercial vehicle trailer and operates there independently of the system pressure ps supplied via the coupling point. By contrast, a pneumatic trailer braking system can be supplied with the system pressure ps via the coupling point of the commercial vehicle trailer. It is also contemplated for a pneumatic suspension system to be operated at the same time via said central pressure connection in order to carry out additional pneumatic functions in the commercial vehicle trailer.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.